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Old 12-21-2014, 11:32 AM   #1
Sport/Truck
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Bad rings or Valve guides?

I'm looking at a 93 chevy 3/4 ton truck w/ 80k miles. it has sat for over a year. It smokes terrible and won't idle and has some hesitation while driving.

Here's what I think is going on, and please let me know how to confirm my theory.

1. idle issue: I think it's a combination of bad fuel, gummed up carb (throttle body) or fouled plugs.

2. Smoke: I've pulled the oil fill cap and check for blow by. Seems to be non-existent. And someone was saying this year model is notorious for leaking valve guides.

I talked to some mechanic friends and they said I should add ATF or Marvel mystery oil to the crank case. I had my Father in law do this while I was out of town and when I got back I started it up and no apparent smoke? So the apparently this cleaned up the rings to allow them to seal?

How can I tell what is wrong with this truck so I can fix it.
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Last edited by Sport/Truck; 12-21-2014 at 12:53 PM.
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Old 12-21-2014, 12:52 PM   #2
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Re: Bad rings or Valve guides?

at 80K miles, I'd doubt it's rings, unless it never had an oil change? Are you using fuel that's been in it for a year? Kinda sounds like you already have it half fixed, if the smoking problem is gone..........I'd have fresh fuel, oil change and plug change on my to-do list for the truck.
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Old 12-22-2014, 12:33 PM   #3
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Re: Bad rings or Valve guides?

I topped off the fuel with only a 1/4 tank and added some fuel conditioner to remove water.
I'll try to get it warmed up and see if the smoke is in fact gone.
(only started it and noticed no smoke).
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Old 12-22-2014, 01:54 PM   #4
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Re: Bad rings or Valve guides?

Keep us posted.........
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Old 12-22-2014, 10:07 PM   #5
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Re: Bad rings or Valve guides?

Hey, Dean, I just have a couple of "seat of the pants" guesses. My newest truck is a '91 so not sure if this will help, and only my '91 4 banger has TBI.

My rough rule of thumb is that under a high vacuum situation like a closed choke(carbureted obviously) or under decelleration blue smoke can indicate weak valve guides. If there is blue smoke under accelleration it can mean weak rings. Rings show up in a compression test, guides won't. Worn guides are possible even with good compression.

The ATF and all mentioned above are legit methods to free stuck rings in engines that have been sitting a long time, and it may be what this engine needed!

DAC
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Old 12-24-2014, 06:42 PM   #6
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Re: Bad rings or Valve guides?

Quote:
Originally Posted by GMCDAC View Post
Hey, Dean, I just have a couple of "seat of the pants" guesses. My newest truck is a '91 so not sure if this will help, and only my '91 4 banger has TBI.

My rough rule of thumb is that under a high vacuum situation like a closed choke(carbureted obviously) or under decelleration blue smoke can indicate weak valve guides. If there is blue smoke under accelleration it can mean weak rings. Rings show up in a compression test, guides won't. Worn guides are possible even with good compression.

The ATF and all mentioned above are legit methods to free stuck rings in engines that have been sitting a long time, and it may be what this engine needed!

DAC
Dac, Do you remember the name of the stuff that's been used forever to clean the top end of engines? I can't think of it right now.
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Old 12-24-2014, 06:50 PM   #7
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Re: Bad rings or Valve guides?

Got IT! It's called SeaFoam...
This stuff out does anything I've ever used.

Pour it down the Carb. while the engine is running, it cleans everythin up. Gunk, Dirty sludge, stuck valves and if the seals aren't too dried out it will seal them up too.
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Old 12-25-2014, 11:41 PM   #8
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Re: Bad rings or Valve guides?

I just had to do this on our Rodeo, was trying to decipher what was killing this cylinder, which came up with both a bad coil pack and bad injector. It's easy enough to check if you are going to replace plugs, I would verify compression, @ least 2 readings, when you pull plugs keep them in order to try and pin point if they are fuel or oil fouled, you should be able to tell, here is a pick of a fuel fouled plug it looked oil but you could smell the fuel. Once the injector came up to operating temp, it would just pour out, this was on a 6 cyl. guess which was fouling out.


I had a average of @180 psi. on all 6, so worked my way to spark then to fuel, but read your plugs they will tell you a lot...


When the seals or rings go you can see the black tarish gummy look to them, good luck, tells us what you came up with. Yes usually the 2 back cylinders seals go bad on these.

Alex
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Old 12-26-2014, 09:23 AM   #9
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Re: Bad rings or Valve guides?

When I do plug changes, I like to write the cylinder # on the tab of the box the plugs came in. #3 and 5 in my 402 have been oil fouling plugs since it was rebuilt. That helped identify the problem, but the builder wouldn't honor the warranty anyway............
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